package ar.com.hjg.pngj;

import ar.com.hjg.pngj.chunks.ChunkRaw;

/**
 * Parses a PNG chunk, consuming bytes in one mode: {@link ChunkReaderMode#BUFFER}, {@link ChunkReaderMode#PROCESS}, {@link ChunkReaderMode#SKIP}.
 * <p>
 * It calls {@link #chunkDone()} when done. Also calls {@link #processData(byte[], int, int)} if <code>PROCESS</code> mode. Apart from thas, it's totally agnostic (it doesn't know
 * about IDAT chunks, or PNG general structure)
 * <p>
 * The object wraps a ChunkRaw instance (content filled only if BUFFER mode); it should be short lived (one instance created for each chunk, and discarded after reading), but the
 * wrapped chunkRaw can be (usually is) long lived.
 */
public abstract class ChunkReader {

  /**
   * see {@link ChunkReaderMode}
   */
  public final ChunkReaderMode mode;
  private final ChunkRaw chunkRaw;

  private boolean crcCheck; // by default, this is false for SKIP, true elsewhere

  /**
   * How many bytes have been read for this chunk, data only
   */
  protected int read = 0;
  private int crcn = 0; // how many bytes have been read from crc

  /**
   * Modes of ChunkReader chunk processing.
   */
  public enum ChunkReaderMode {
    /**
     * Stores full chunk data in buffer
     */
    BUFFER,
    /**
     * Does not store content, processes on the fly, calling processData() for each partial read
     */
    PROCESS,
    /**
     * Does not store nor process - implies crcCheck=false (by default).
     */
    SKIP;
  }

  /**
   * The constructor creates also a chunkRaw, preallocated if mode = ChunkReaderMode.BUFFER
   * 
   * @param clen
   * @param id
   * @param offsetInPng Informational, is stored in chunkRaw
   * @param mode
   */
  public ChunkReader(int clen, String id, long offsetInPng, ChunkReaderMode mode) {
    if (mode == null || id.length() != 4 || clen < 0)
      throw new PngjExceptionInternal("Bad chunk paramenters: " + mode);
    this.mode = mode;
    chunkRaw = new ChunkRaw(clen, id, mode == ChunkReaderMode.BUFFER);
    chunkRaw.setOffset(offsetInPng);
    this.crcCheck = mode == ChunkReaderMode.SKIP ? false : true; // can be changed with setter
  }

  /**
   * Returns raw chunk (data can be empty or not, depending on ChunkReaderMode)
   * 
   * @return Raw chunk - never null
   */
  public ChunkRaw getChunkRaw() {
    return chunkRaw;
  }

  /**
   * Consumes data for the chunk (data and CRC). This never consumes more bytes than for this chunk.
   * 
   * In HOT_PROCESS can call processData() (not more than once)
   * 
   * If this ends the chunk (included CRC) it checks CRC (if checking) and calls chunkDone()
   * 
   * @param buf
   * @param off
   * @param len
   * @return How many bytes have been consumed
   */
  public final int feedBytes(byte[] buf, int off, int len) {
    if (len == 0)
      return 0;
    if (len < 0)
      throw new PngjException("negative length??");
    if (read == 0 && crcn == 0 && crcCheck)
      chunkRaw.updateCrc(chunkRaw.idbytes, 0, 4); // initializes crc calculation with the Chunk ID
    int bytesForData = chunkRaw.len - read; // bytesForData : bytes to be actually read from chunk data
    if (bytesForData > len)
      bytesForData = len;
    // we want to call processData even for empty chunks (IEND:bytesForData=0) at least once
    if (bytesForData > 0 || crcn == 0) {
      // in buffer mode we compute the CRC at the end
      if (crcCheck && mode != ChunkReaderMode.BUFFER && bytesForData > 0)
        chunkRaw.updateCrc(buf, off, bytesForData);

      if (mode == ChunkReaderMode.BUFFER) {
        // just copy the contents to the internal buffer
        if (chunkRaw.data != buf && bytesForData > 0) {
          // if the buffer passed if the same as this one, we don't copy the caller should know what he's doing
          System.arraycopy(buf, off, chunkRaw.data, read, bytesForData);
        }
      } else if (mode == ChunkReaderMode.PROCESS) {
        processData(read, buf, off, bytesForData);
      } else {
        // mode == ChunkReaderMode.SKIP; nothing to do
      }
      read += bytesForData;
      off += bytesForData;
      len -= bytesForData;
    }
    int crcRead = 0;
    if (read == chunkRaw.len) { // data done - read crc?
      crcRead = 4 - crcn;
      if (crcRead > len)
        crcRead = len;
      if (crcRead > 0) {
        if (buf != chunkRaw.crcval)
          System.arraycopy(buf, off, chunkRaw.crcval, crcn, crcRead);
        crcn += crcRead;
        if (crcn == 4) {
          if (crcCheck) {
            if (mode == ChunkReaderMode.BUFFER) { // in buffer mode we compute the CRC on one single call
              chunkRaw.updateCrc(chunkRaw.data, 0, chunkRaw.len);
            }
            chunkRaw.checkCrc();
          }
          chunkDone();
        }
      }
    }
    return bytesForData + crcRead;
  }

  /**
   * Chunks has been read
   * 
   * @return true if we have read all chunk, including trailing CRC
   */
  public final boolean isDone() {
    return crcn == 4; // has read all 4 bytes from the crc
  }

  /**
   * Determines if CRC should be checked. This should be called before starting reading.
   * 
   * @param crcCheck
   */
  public void setCrcCheck(boolean crcCheck) {
    if (read != 0 && crcCheck && !this.crcCheck)
      throw new PngjException("too late!");
    this.crcCheck = crcCheck;
  }

  /**
   * This method will only be called in PROCESS mode, probably several times, each time with a new fragment of data inside the chunk. For chunks with zero-length data, this will
   * still be called once.
   * 
   * It's guaranteed that the data corresponds exclusively to this chunk data (no crc, no data from no other chunks, )
   * 
   * @param offsetInchunk data bytes that had already been read/processed for this chunk
   * @param buf
   * @param off
   * @param len
   */
  protected abstract void processData(int offsetInchunk, byte[] buf, int off, int len);

  /**
   * This method will be called (in all modes) when the full chunk -including crc- has been read
   */
  protected abstract void chunkDone();

  public boolean isFromDeflatedSet() {
    return false;
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((chunkRaw == null) ? 0 : chunkRaw.hashCode());
    return result;
  }

  /**
   * Equality (and hash) is basically delegated to the ChunkRaw
   */
  @Override
  public boolean equals(Object obj) { // delegates to chunkraw
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    ChunkReader other = (ChunkReader) obj;
    if (chunkRaw == null) {
      if (other.chunkRaw != null)
        return false;
    } else if (!chunkRaw.equals(other.chunkRaw))
      return false;
    return true;
  }

  @Override
  public String toString() {
    return chunkRaw.toString();
  }

}
